The present invention relates to vehicle crash sensors in general and to sensors which detect a collision with a pedestrian in particular.
Improvements in the structural design of automobiles, combined with passive safety systems such as seat belts, and active safety systems such as air bags and seatbelt retractors, have greatly decreased death and injury to automobile occupants resulting from a car crash. The active safety systems respond to crash sensors that detect the onset of a vehicle crash, and activate or deploy devices to minimize vehicle occupant injury during the crash.
A vehicle collision is not only a hazard to the vehicle occupants, but in the case of a collision with a pedestrian, the pedestrian may be gravely injured or killed. Recently there have been efforts to develop deployable safety systems that are designed to benefit the pedestrian during a vehicle-pedestrian collision. These systems deploy actuators that raise the vehicle hood, or deploy an airbag to reduce injury to the pedestrian's head. Another type of collision that may be relatively benign is a collision with an animal such as a deer. The major hazard of this type of collision is that the animal may ride up over the hood of the vehicle and crash through the front windshield. Active safety systems that respond to the onset of a vehicle-animal collision are being considered.
U.S. Pat. No. 6,784,792 B2 discloses using piezoelectric film sensors to detect pressure and deformation caused by impact with a pedestrian, and comparing the sensor output signals to a reference quantity to derive a first decision criteria, and discloses deriving a second criteria due to the change in velocity or acceleration of the vehicle. Piezoelectric strips have been used to detect the onset of a crash, such as disclosed in U.S. Pat. No. 6,559,763 B2. Measurement of strain energy to detect a side impact using a piezoelectric sensor is disclosed in U.S. Pat. No. 5,797,623.
Using a piezoelectric film to detect accelerations produced by hydraulic percussion devices is known from U.S. Pat. No. 6,737,981 B2. The frequency and amplitude of a magnetorestrictive sensor have been analyzed to determine the position of the crash in the transverse direction along a stress conducting member, as in U.S. Pat. No. 6,329,910 B1.
Both a vehicle-pedestrian collision, and a vehicle-animal collision are similar in that the vehicle impacts with a relatively low mass soft tissue object. Sensors are needed which can differentiate this type of collision from collisions with large massive objects, or collisions with less massive but rigid objects, so that in each case the deployment or non-deployment of active safety systems can be optimized.